1. Field of the Invention
The present invention relates to the reading of fingerprints, and more particularly concerns an unique configuration of an input prism assembly and a precisely controlled scanning mirror.
2. Description of Related Art
Fingerprint identification is becoming increasingly automated, and as advantages of automatic fingerprint identification systems become more apparent through widespread use, automated fingerprint identification systems are becoming more common and more widely used. Automated fingerprint identification systems input an electronic representation of an unknown fingerprint for use in selection of one or more matching prints from a massive body of stored electronic representations of many fingerprints. Yet, despite the extent and sophistication of automated fingerprint matching, fingerprints still are captured and recorded by old and conventional procedures utilizing ink, ink pad, and roller to provide an inked impression which is scanned to form a digital electronic representation for storage or comparison. These conventional procedures are inconvenient, slow, and, in many cases, inefficient. They frequently fail to record adequate definition of certain details, singularities and minutiae, that are employed in fingerprint identification and matching processes.
Various types of optical systems have been suggested for automatically capturing and recording a print without use of card and ink, but these systems fail to provide a print record that will meet established criteria, such as specifications established by the Federal Bureau of Investigation. These criteria must be met for efficient and effective input to the automated print identification and matching equipment. Prior optical reading systems produce output images that are unacceptably distorted and lacking in satisfactory definition and resolution.
Prior optical fingerprint imaging apparatus are difficult or inconvenient for use, require special handling, finger positioning and finger motion techniques, or are expensive and complex, while failing to provide fingerprint images that meet established criteria. For example, the patent to Fowler et al., U.S. Pat. No. 4,537,484, requires a finger to be placed in a hollow cylindrical trough and has a driven light source that rotates around the trough. The patent to Yang, U.S. Pat. No. 5,109,427, employs a complex system for deriving a hologram that requires complicated and expensive optics. The imaging device of the patent to Rachlin, U.S. Pat. No. 4,925,300, involves a conical transparent surface that can accept only a single finger at a time. The patent to Froelich, U.S. Pat. No. 4,690,554, employs auto correlation requiring a pair of independent identical relay lens systems. The patents to Rios, U.S. Pat. Nos. 4,568,178 and 4,652,116, each employs a camera with one or more lens to photocopy impressions made by ridges on the tips of fingers.
These patents provide for arrangements to contact the finger that are for the most part significantly different than the widely and commonly used inked pad surface. The long used inked pad technique makes a slap print by placing all four fingers flat on a single surface or makes a roll print by individually rolling each of the several fingers of a hand over the surface about the finger longitudinal axis. Persons experienced in obtaining fingerprints by the standard ink and pad format require retraining and may very well experience difficulty in using different types of input devices such as the above-identified optical input systems. This may result in greater time for taking fingerprints and also may increase the making of unacceptable prints. The prior art fails to provide a finger pressing surface having a front edge that is at an upper and forwardmost portion of the surface and as such is readily accessible to a finger to be placed upon the pressure receiving surface. In taking the print of a single finger, the remaining fingers of the same hand must be bent so that a reasonable part of the length of the single finger being printed can be pressed against a print receiving surface and no other portion of the apparatus will interfere with the knuckles of the bent fingers. Prior optical readers do not provide for such familiar simplified and convenient access of a single finger.
Optical readers require light sources that provide a strong illuminating beam and use lens systems and electronics which cooperate with the finger receiving surface to provide a fingerprint output. Packaging of the illumination source, image transmitting optics, and electronics is difficult to achieve without sacrificing convenience of finger access or without including parts that interfere with knuckles of the fingers not being printed. It is even more difficult to locate non-interfering light source and transmitting optics where total internal reflection at the platen requires certain critical angles of illumination.
Some prior optical systems have employed a large mirror to control direction and position of light exiting the imaging prism. Such a mirror requires a kinematic mount that needs to be adjusted during product shipment. Cost and labor for such mirror mounting is great. Realignment of the mirror at the installation site is not acceptable.
Accordingly, it is an object of the present invention to provide for optical fingerprint imaging that minimizes or avoids problems of the prior art.